SlideShare uma empresa Scribd logo
1 de 8
Baixar para ler offline
Chapter 7

Electrically Symmetric
Poly(Phenylene Acetylene)
Diodes
             Journal Molecular Crystals and Liquid Crystals (1994)
                              Vol. 256, pp. 555{561.

    S. A. Jeglinski, M. E. Hollier, J. F. Gold, and Z. V. Vardeny


        University of Utah, Physics Department, Salt Lake City, UT 84112


                          Y. Ding and T. Barton


          Iowa State University, Chemistry Department, Ames, IA 50011




Abstract
A diode has been fabricated with poly(phenylene acetylene) [PPA] as the elec-
troluminescent polymer. The device exhibited an unusual symmetric (positive
and negative bias) I{V characteristic and electroluminescent output. These ex-
perimental results are discussed in terms of tunneling of electrons and holes via
localized states.

Introduction
Luminescent conjugated polymers have recently attracted considerable interest
because of their use as active materials in light-emitting devices (LEDs) [1].
Operation as such depends upon the ability to inject into the polymer electrons
and holes, which then recombine to emit light.

                                        1
CHAPTER 7.      ELECTRICALLY SYMMETRIC PPA DIODES                             2

Experimental Setup and Procedure
A PPA solution was made by mixing powder with CHCl3 (about 50 ml/mg).
The solution was thoroughly dissolved by immersion in an ultrasonic agitator.
The solution was then
ltered into clean glassware with a 0.2 m Nalge syringe
lter. Semitransparent ITO-coated silica plates ( 200 
/sq, 25 nm thick ITO
on 1.5 mm thick silica) were procured and cut with a diamond saw into ap-
proximately 12 2 12 mm squares. Approximately one-third of the ITO (a 4
mm strip on one end) was removed with a standard solution of aqua regia. The
substrates (2/3 ITO-silica, 1/3 silica-only) were then thoroughly cleaned by ul-
trasonic agitation in a CHCl3 bath several times, with a
nal wash in distilled
de-ionized water.
    Fabrication was accomplished by spin-casting the
ltered PPA solution onto
the prepared substrates, forming a polymer layer about 1000-1500  thick. The
                                                                 A
spin-casting and handling of the polymer/ITO substrate were performed in a
glove-box purged with nitrogen. Part of the polymer was then stripped o with
a solvent-dipped cotton swab. Aluminum electrodes were thermally evaporated
onto the PPA/ITO substrates in a vacuum chamber with an operating pressure
of about 8 2 1006 Torr. Figure 6.1 shows the
nal geometry of the prepared
device. The stripping procedures described above helped ensure that there was
no inadvertent shortening between the Al and the ITO.
    A Keithley 236 source-measure-unit (SMU) was interfaced to a PC and con-
nected to the aluminum electrodes with microclips. The SMU was then used to
bias the ITO layer positively and negatively with respect to the Al electrodes.
Swept measurements were made in the range from -20 to +20 Volts. All han-
dling and measurements were made either in the nitrogen-purged glove-box or
in an evacuated cryostat.

Result
A variety of results were obtained. Many devices never exhibited anything other
than resistive behavior. Some devices exhibited a nonlinear I{V characteristic
after the device was burned in by applying a constant voltage for a rela-
tively long period of time (several minutes), during which time the electrical
properties eventually settled into a repeatable pattern. Some devices exhib-
ited a well-de
ned nonlinear I{V characteristic immediately, but often would
fail rapidly unless operated while immersed in liquid nitrogen, probably due to
excess power dissipation in the device. Two of the devices constructed showed
a symmetric electrical characteristic, i.e., equal but opposite forward-bias and
reverse-bias behavior. This result is shown in Figure 6.2.

Mais conteúdo relacionado

Mais procurados

Physica curckts
Physica curcktsPhysica curckts
Physica curckts
12B-129-El
 
Marking scheme of question paper 2013 phyics set1_dl
Marking scheme of question paper 2013 phyics set1_dlMarking scheme of question paper 2013 phyics set1_dl
Marking scheme of question paper 2013 phyics set1_dl
KV no 1 AFS Jodhpur raj.
 
L 07(gdr)(et) ((ee)nptel)
L 07(gdr)(et) ((ee)nptel)L 07(gdr)(et) ((ee)nptel)
L 07(gdr)(et) ((ee)nptel)
Pradeep Godara
 
E L E C T R I C A L C I R C U I T S A N A L Y S I S J N T U M O D E L P ...
E L E C T R I C A L  C I R C U I T S  A N A L Y S I S  J N T U  M O D E L  P ...E L E C T R I C A L  C I R C U I T S  A N A L Y S I S  J N T U  M O D E L  P ...
E L E C T R I C A L C I R C U I T S A N A L Y S I S J N T U M O D E L P ...
guest3f9c6b
 
Elect machine total_2012
Elect machine total_2012Elect machine total_2012
Elect machine total_2012
masterslide
 
Paper of Tahesin Samira Delwar_ IEEE Conf 2014
Paper of Tahesin Samira Delwar_ IEEE  Conf 2014Paper of Tahesin Samira Delwar_ IEEE  Conf 2014
Paper of Tahesin Samira Delwar_ IEEE Conf 2014
TAHESIN SAMIRA DELWAR
 

Mais procurados (19)

Physica curckts
Physica curcktsPhysica curckts
Physica curckts
 
Marking scheme of question paper 2013 phyics set1_dl
Marking scheme of question paper 2013 phyics set1_dlMarking scheme of question paper 2013 phyics set1_dl
Marking scheme of question paper 2013 phyics set1_dl
 
Distortionless Transmission Line
Distortionless Transmission LineDistortionless Transmission Line
Distortionless Transmission Line
 
Chapter 1 pt 2
Chapter 1 pt 2Chapter 1 pt 2
Chapter 1 pt 2
 
L 07(gdr)(et) ((ee)nptel)
L 07(gdr)(et) ((ee)nptel)L 07(gdr)(et) ((ee)nptel)
L 07(gdr)(et) ((ee)nptel)
 
Class 12 Cbse Physics Sample Paper 2010 Model 3
Class 12 Cbse Physics Sample Paper 2010 Model 3Class 12 Cbse Physics Sample Paper 2010 Model 3
Class 12 Cbse Physics Sample Paper 2010 Model 3
 
Dielectrics
DielectricsDielectrics
Dielectrics
 
Cbse 12 Class Physics Sample Paper 2010 Model 2
Cbse 12 Class Physics Sample Paper 2010 Model 2Cbse 12 Class Physics Sample Paper 2010 Model 2
Cbse 12 Class Physics Sample Paper 2010 Model 2
 
ijaerv10n9spl_473
ijaerv10n9spl_473ijaerv10n9spl_473
ijaerv10n9spl_473
 
E L E C T R I C A L C I R C U I T S A N A L Y S I S J N T U M O D E L P ...
E L E C T R I C A L  C I R C U I T S  A N A L Y S I S  J N T U  M O D E L  P ...E L E C T R I C A L  C I R C U I T S  A N A L Y S I S  J N T U  M O D E L  P ...
E L E C T R I C A L C I R C U I T S A N A L Y S I S J N T U M O D E L P ...
 
EEE 7
EEE 7EEE 7
EEE 7
 
Elect machine total_2012
Elect machine total_2012Elect machine total_2012
Elect machine total_2012
 
SPM PHYSICS FORM 5 radioactivity
SPM PHYSICS FORM 5  radioactivitySPM PHYSICS FORM 5  radioactivity
SPM PHYSICS FORM 5 radioactivity
 
My2522202224
My2522202224My2522202224
My2522202224
 
SPM PHYSICS FORM 5 electronics
SPM PHYSICS FORM 5 electronicsSPM PHYSICS FORM 5 electronics
SPM PHYSICS FORM 5 electronics
 
Digi ana total 2012
Digi ana total 2012Digi ana total 2012
Digi ana total 2012
 
Paper of Tahesin Samira Delwar_ IEEE Conf 2014
Paper of Tahesin Samira Delwar_ IEEE  Conf 2014Paper of Tahesin Samira Delwar_ IEEE  Conf 2014
Paper of Tahesin Samira Delwar_ IEEE Conf 2014
 
PHYSICS XII SAMPLE PAPER BY ATC
PHYSICS XII SAMPLE PAPER BY ATCPHYSICS XII SAMPLE PAPER BY ATC
PHYSICS XII SAMPLE PAPER BY ATC
 
Lecture 16
Lecture 16Lecture 16
Lecture 16
 

Destaque (6)

Polystyrene
PolystyrenePolystyrene
Polystyrene
 
Project report on polystyrene (ps)
Project report on polystyrene (ps)Project report on polystyrene (ps)
Project report on polystyrene (ps)
 
POLYSTYRENE
POLYSTYRENEPOLYSTYRENE
POLYSTYRENE
 
polystyrene
polystyrenepolystyrene
polystyrene
 
Symmetry and point group theory 260912
Symmetry and point group theory 260912Symmetry and point group theory 260912
Symmetry and point group theory 260912
 
LinkedIn SlideShare: Knowledge, Well-Presented
LinkedIn SlideShare: Knowledge, Well-PresentedLinkedIn SlideShare: Knowledge, Well-Presented
LinkedIn SlideShare: Knowledge, Well-Presented
 

Semelhante a Electrically Symmetric Poly(Phenylene Acetylene) Diodes

Senior Thesis Presentation
Senior Thesis PresentationSenior Thesis Presentation
Senior Thesis Presentation
Bryan McLaren
 
Polarization bremsstrahlung on atoms, plasmas, nanostructures and solids
Polarization bremsstrahlung on atoms, plasmas, nanostructures and solidsPolarization bremsstrahlung on atoms, plasmas, nanostructures and solids
Polarization bremsstrahlung on atoms, plasmas, nanostructures and solids
Springer
 
2nd Year Poster-Jonathan Wood
2nd Year Poster-Jonathan Wood2nd Year Poster-Jonathan Wood
2nd Year Poster-Jonathan Wood
Jonathan Wood
 

Semelhante a Electrically Symmetric Poly(Phenylene Acetylene) Diodes (20)

Eng4
Eng4Eng4
Eng4
 
A Technique To Model A Frequency Mixer
A Technique To Model A Frequency MixerA Technique To Model A Frequency Mixer
A Technique To Model A Frequency Mixer
 
STUDY OF THE EQUIVALENT CIRCUIT OF A DYESENSITIZED SOLAR CELLS
STUDY OF THE EQUIVALENT CIRCUIT OF A DYESENSITIZED SOLAR CELLSSTUDY OF THE EQUIVALENT CIRCUIT OF A DYESENSITIZED SOLAR CELLS
STUDY OF THE EQUIVALENT CIRCUIT OF A DYESENSITIZED SOLAR CELLS
 
STUDY OF THE EQUIVALENT CIRCUIT OF A DYESENSITIZED SOLAR CELLS
STUDY OF THE EQUIVALENT CIRCUIT OF A DYESENSITIZED SOLAR CELLSSTUDY OF THE EQUIVALENT CIRCUIT OF A DYESENSITIZED SOLAR CELLS
STUDY OF THE EQUIVALENT CIRCUIT OF A DYESENSITIZED SOLAR CELLS
 
A detailed modeling of photovoltaic module matlab
A detailed modeling of photovoltaic module   matlabA detailed modeling of photovoltaic module   matlab
A detailed modeling of photovoltaic module matlab
 
Modelling and Analysis of Single Diode Photovoltaic Module using MATLAB/Simulink
Modelling and Analysis of Single Diode Photovoltaic Module using MATLAB/SimulinkModelling and Analysis of Single Diode Photovoltaic Module using MATLAB/Simulink
Modelling and Analysis of Single Diode Photovoltaic Module using MATLAB/Simulink
 
Senior Thesis Presentation
Senior Thesis PresentationSenior Thesis Presentation
Senior Thesis Presentation
 
BACK to BASIC 7.pdf
BACK to BASIC 7.pdfBACK to BASIC 7.pdf
BACK to BASIC 7.pdf
 
Et36891896
Et36891896Et36891896
Et36891896
 
P01052131135
P01052131135P01052131135
P01052131135
 
1st paper
1st paper1st paper
1st paper
 
Dye Solar Cells - DSC - Impedance Measurements
Dye Solar Cells - DSC - Impedance MeasurementsDye Solar Cells - DSC - Impedance Measurements
Dye Solar Cells - DSC - Impedance Measurements
 
Diodes and semiconductors - an introduction
Diodes and semiconductors - an introductionDiodes and semiconductors - an introduction
Diodes and semiconductors - an introduction
 
A Detailed Explanation of Solenoid Force
A Detailed Explanation of Solenoid ForceA Detailed Explanation of Solenoid Force
A Detailed Explanation of Solenoid Force
 
THE EFFECT OF INTERFACE MODIFICATION BY PEDOT: PSS ON THE HOLE MOBILITY OF TH...
THE EFFECT OF INTERFACE MODIFICATION BY PEDOT: PSS ON THE HOLE MOBILITY OF TH...THE EFFECT OF INTERFACE MODIFICATION BY PEDOT: PSS ON THE HOLE MOBILITY OF TH...
THE EFFECT OF INTERFACE MODIFICATION BY PEDOT: PSS ON THE HOLE MOBILITY OF TH...
 
Electric arc furnec
Electric arc furnecElectric arc furnec
Electric arc furnec
 
Some Aspects of Stress Distribution and Effect of Voids Having Different Gase...
Some Aspects of Stress Distribution and Effect of Voids Having Different Gase...Some Aspects of Stress Distribution and Effect of Voids Having Different Gase...
Some Aspects of Stress Distribution and Effect of Voids Having Different Gase...
 
Mu2522002204
Mu2522002204Mu2522002204
Mu2522002204
 
Polarization bremsstrahlung on atoms, plasmas, nanostructures and solids
Polarization bremsstrahlung on atoms, plasmas, nanostructures and solidsPolarization bremsstrahlung on atoms, plasmas, nanostructures and solids
Polarization bremsstrahlung on atoms, plasmas, nanostructures and solids
 
2nd Year Poster-Jonathan Wood
2nd Year Poster-Jonathan Wood2nd Year Poster-Jonathan Wood
2nd Year Poster-Jonathan Wood
 

Mais de Jeffrey Gold

Mais de Jeffrey Gold (16)

MarCom/Branding Portfolio (Communication Designer: Jeffrey Gold)
MarCom/Branding Portfolio (Communication Designer: Jeffrey Gold)MarCom/Branding Portfolio (Communication Designer: Jeffrey Gold)
MarCom/Branding Portfolio (Communication Designer: Jeffrey Gold)
 
Usability Considerations in Website Design: Lessons from Architectural Design...
Usability Considerations in Website Design: Lessons from Architectural Design...Usability Considerations in Website Design: Lessons from Architectural Design...
Usability Considerations in Website Design: Lessons from Architectural Design...
 
The Importance of Arts In Education
The Importance of Arts In EducationThe Importance of Arts In Education
The Importance of Arts In Education
 
Short Lifetimes of Light Emitting Polymers
Short Lifetimes of Light Emitting PolymersShort Lifetimes of Light Emitting Polymers
Short Lifetimes of Light Emitting Polymers
 
Knocking on the Devil’s Door: A Naive Introduction To Quantum Mechanics
Knocking on the Devil’s Door: A Naive Introduction To Quantum MechanicsKnocking on the Devil’s Door: A Naive Introduction To Quantum Mechanics
Knocking on the Devil’s Door: A Naive Introduction To Quantum Mechanics
 
Complementary Sets of Systems of Congruences
Complementary Sets of Systems of CongruencesComplementary Sets of Systems of Congruences
Complementary Sets of Systems of Congruences
 
A Characterization of Twin Prime Pairs
A Characterization of Twin Prime PairsA Characterization of Twin Prime Pairs
A Characterization of Twin Prime Pairs
 
Vector Products Revisited: A New and Efficient Method of Proving Vector Ident...
Vector Products Revisited: A New and Efficient Method of Proving Vector Ident...Vector Products Revisited: A New and Efficient Method of Proving Vector Ident...
Vector Products Revisited: A New and Efficient Method of Proving Vector Ident...
 
Remodulization of Congruences
Remodulization of CongruencesRemodulization of Congruences
Remodulization of Congruences
 
A Novel Solution Of Linear Congruences
A Novel Solution Of Linear CongruencesA Novel Solution Of Linear Congruences
A Novel Solution Of Linear Congruences
 
Resume - Communication Designer: Jeffrey Gold
Resume - Communication Designer: Jeffrey GoldResume - Communication Designer: Jeffrey Gold
Resume - Communication Designer: Jeffrey Gold
 
Technical Illustrations
Technical IllustrationsTechnical Illustrations
Technical Illustrations
 
Graphic Design Portfolio - Designer: Jeffrey Gold
Graphic Design Portfolio - Designer: Jeffrey GoldGraphic Design Portfolio - Designer: Jeffrey Gold
Graphic Design Portfolio - Designer: Jeffrey Gold
 
Story Structure
Story StructureStory Structure
Story Structure
 
Is Gravitation A Result Of Asymmetric Coulomb Charge Interactions?
Is Gravitation A Result Of Asymmetric Coulomb Charge Interactions?Is Gravitation A Result Of Asymmetric Coulomb Charge Interactions?
Is Gravitation A Result Of Asymmetric Coulomb Charge Interactions?
 
On a Conjecture of Erdös
On a Conjecture of ErdösOn a Conjecture of Erdös
On a Conjecture of Erdös
 

Último

Finding Java's Hidden Performance Traps @ DevoxxUK 2024
Finding Java's Hidden Performance Traps @ DevoxxUK 2024Finding Java's Hidden Performance Traps @ DevoxxUK 2024
Finding Java's Hidden Performance Traps @ DevoxxUK 2024
Victor Rentea
 
+971581248768>> SAFE AND ORIGINAL ABORTION PILLS FOR SALE IN DUBAI AND ABUDHA...
+971581248768>> SAFE AND ORIGINAL ABORTION PILLS FOR SALE IN DUBAI AND ABUDHA...+971581248768>> SAFE AND ORIGINAL ABORTION PILLS FOR SALE IN DUBAI AND ABUDHA...
+971581248768>> SAFE AND ORIGINAL ABORTION PILLS FOR SALE IN DUBAI AND ABUDHA...
?#DUbAI#??##{{(☎️+971_581248768%)**%*]'#abortion pills for sale in dubai@
 
Why Teams call analytics are critical to your entire business
Why Teams call analytics are critical to your entire businessWhy Teams call analytics are critical to your entire business
Why Teams call analytics are critical to your entire business
panagenda
 
Modular Monolith - a Practical Alternative to Microservices @ Devoxx UK 2024
Modular Monolith - a Practical Alternative to Microservices @ Devoxx UK 2024Modular Monolith - a Practical Alternative to Microservices @ Devoxx UK 2024
Modular Monolith - a Practical Alternative to Microservices @ Devoxx UK 2024
Victor Rentea
 

Último (20)

Finding Java's Hidden Performance Traps @ DevoxxUK 2024
Finding Java's Hidden Performance Traps @ DevoxxUK 2024Finding Java's Hidden Performance Traps @ DevoxxUK 2024
Finding Java's Hidden Performance Traps @ DevoxxUK 2024
 
MINDCTI Revenue Release Quarter One 2024
MINDCTI Revenue Release Quarter One 2024MINDCTI Revenue Release Quarter One 2024
MINDCTI Revenue Release Quarter One 2024
 
DEV meet-up UiPath Document Understanding May 7 2024 Amsterdam
DEV meet-up UiPath Document Understanding May 7 2024 AmsterdamDEV meet-up UiPath Document Understanding May 7 2024 Amsterdam
DEV meet-up UiPath Document Understanding May 7 2024 Amsterdam
 
+971581248768>> SAFE AND ORIGINAL ABORTION PILLS FOR SALE IN DUBAI AND ABUDHA...
+971581248768>> SAFE AND ORIGINAL ABORTION PILLS FOR SALE IN DUBAI AND ABUDHA...+971581248768>> SAFE AND ORIGINAL ABORTION PILLS FOR SALE IN DUBAI AND ABUDHA...
+971581248768>> SAFE AND ORIGINAL ABORTION PILLS FOR SALE IN DUBAI AND ABUDHA...
 
Why Teams call analytics are critical to your entire business
Why Teams call analytics are critical to your entire businessWhy Teams call analytics are critical to your entire business
Why Teams call analytics are critical to your entire business
 
[BuildWithAI] Introduction to Gemini.pdf
[BuildWithAI] Introduction to Gemini.pdf[BuildWithAI] Introduction to Gemini.pdf
[BuildWithAI] Introduction to Gemini.pdf
 
TrustArc Webinar - Unlock the Power of AI-Driven Data Discovery
TrustArc Webinar - Unlock the Power of AI-Driven Data DiscoveryTrustArc Webinar - Unlock the Power of AI-Driven Data Discovery
TrustArc Webinar - Unlock the Power of AI-Driven Data Discovery
 
Modular Monolith - a Practical Alternative to Microservices @ Devoxx UK 2024
Modular Monolith - a Practical Alternative to Microservices @ Devoxx UK 2024Modular Monolith - a Practical Alternative to Microservices @ Devoxx UK 2024
Modular Monolith - a Practical Alternative to Microservices @ Devoxx UK 2024
 
Exploring Multimodal Embeddings with Milvus
Exploring Multimodal Embeddings with MilvusExploring Multimodal Embeddings with Milvus
Exploring Multimodal Embeddings with Milvus
 
Repurposing LNG terminals for Hydrogen Ammonia: Feasibility and Cost Saving
Repurposing LNG terminals for Hydrogen Ammonia: Feasibility and Cost SavingRepurposing LNG terminals for Hydrogen Ammonia: Feasibility and Cost Saving
Repurposing LNG terminals for Hydrogen Ammonia: Feasibility and Cost Saving
 
Artificial Intelligence Chap.5 : Uncertainty
Artificial Intelligence Chap.5 : UncertaintyArtificial Intelligence Chap.5 : Uncertainty
Artificial Intelligence Chap.5 : Uncertainty
 
Navigating the Deluge_ Dubai Floods and the Resilience of Dubai International...
Navigating the Deluge_ Dubai Floods and the Resilience of Dubai International...Navigating the Deluge_ Dubai Floods and the Resilience of Dubai International...
Navigating the Deluge_ Dubai Floods and the Resilience of Dubai International...
 
Corporate and higher education May webinar.pptx
Corporate and higher education May webinar.pptxCorporate and higher education May webinar.pptx
Corporate and higher education May webinar.pptx
 
Emergent Methods: Multi-lingual narrative tracking in the news - real-time ex...
Emergent Methods: Multi-lingual narrative tracking in the news - real-time ex...Emergent Methods: Multi-lingual narrative tracking in the news - real-time ex...
Emergent Methods: Multi-lingual narrative tracking in the news - real-time ex...
 
Apidays New York 2024 - The Good, the Bad and the Governed by David O'Neill, ...
Apidays New York 2024 - The Good, the Bad and the Governed by David O'Neill, ...Apidays New York 2024 - The Good, the Bad and the Governed by David O'Neill, ...
Apidays New York 2024 - The Good, the Bad and the Governed by David O'Neill, ...
 
CNIC Information System with Pakdata Cf In Pakistan
CNIC Information System with Pakdata Cf In PakistanCNIC Information System with Pakdata Cf In Pakistan
CNIC Information System with Pakdata Cf In Pakistan
 
Apidays New York 2024 - APIs in 2030: The Risk of Technological Sleepwalk by ...
Apidays New York 2024 - APIs in 2030: The Risk of Technological Sleepwalk by ...Apidays New York 2024 - APIs in 2030: The Risk of Technological Sleepwalk by ...
Apidays New York 2024 - APIs in 2030: The Risk of Technological Sleepwalk by ...
 
ICT role in 21st century education and its challenges
ICT role in 21st century education and its challengesICT role in 21st century education and its challenges
ICT role in 21st century education and its challenges
 
MS Copilot expands with MS Graph connectors
MS Copilot expands with MS Graph connectorsMS Copilot expands with MS Graph connectors
MS Copilot expands with MS Graph connectors
 
AXA XL - Insurer Innovation Award Americas 2024
AXA XL - Insurer Innovation Award Americas 2024AXA XL - Insurer Innovation Award Americas 2024
AXA XL - Insurer Innovation Award Americas 2024
 

Electrically Symmetric Poly(Phenylene Acetylene) Diodes

  • 1. Chapter 7 Electrically Symmetric Poly(Phenylene Acetylene) Diodes Journal Molecular Crystals and Liquid Crystals (1994) Vol. 256, pp. 555{561. S. A. Jeglinski, M. E. Hollier, J. F. Gold, and Z. V. Vardeny University of Utah, Physics Department, Salt Lake City, UT 84112 Y. Ding and T. Barton Iowa State University, Chemistry Department, Ames, IA 50011 Abstract A diode has been fabricated with poly(phenylene acetylene) [PPA] as the elec- troluminescent polymer. The device exhibited an unusual symmetric (positive and negative bias) I{V characteristic and electroluminescent output. These ex- perimental results are discussed in terms of tunneling of electrons and holes via localized states. Introduction Luminescent conjugated polymers have recently attracted considerable interest because of their use as active materials in light-emitting devices (LEDs) [1]. Operation as such depends upon the ability to inject into the polymer electrons and holes, which then recombine to emit light. 1
  • 2. CHAPTER 7. ELECTRICALLY SYMMETRIC PPA DIODES 2 Experimental Setup and Procedure A PPA solution was made by mixing powder with CHCl3 (about 50 ml/mg). The solution was thoroughly dissolved by immersion in an ultrasonic agitator. The solution was then
  • 3. ltered into clean glassware with a 0.2 m Nalge syringe
  • 4. lter. Semitransparent ITO-coated silica plates ( 200 /sq, 25 nm thick ITO on 1.5 mm thick silica) were procured and cut with a diamond saw into ap- proximately 12 2 12 mm squares. Approximately one-third of the ITO (a 4 mm strip on one end) was removed with a standard solution of aqua regia. The substrates (2/3 ITO-silica, 1/3 silica-only) were then thoroughly cleaned by ul- trasonic agitation in a CHCl3 bath several times, with a
  • 5. nal wash in distilled de-ionized water. Fabrication was accomplished by spin-casting the
  • 6. ltered PPA solution onto the prepared substrates, forming a polymer layer about 1000-1500 thick. The A spin-casting and handling of the polymer/ITO substrate were performed in a glove-box purged with nitrogen. Part of the polymer was then stripped o with a solvent-dipped cotton swab. Aluminum electrodes were thermally evaporated onto the PPA/ITO substrates in a vacuum chamber with an operating pressure of about 8 2 1006 Torr. Figure 6.1 shows the
  • 7. nal geometry of the prepared device. The stripping procedures described above helped ensure that there was no inadvertent shortening between the Al and the ITO. A Keithley 236 source-measure-unit (SMU) was interfaced to a PC and con- nected to the aluminum electrodes with microclips. The SMU was then used to bias the ITO layer positively and negatively with respect to the Al electrodes. Swept measurements were made in the range from -20 to +20 Volts. All han- dling and measurements were made either in the nitrogen-purged glove-box or in an evacuated cryostat. Result A variety of results were obtained. Many devices never exhibited anything other than resistive behavior. Some devices exhibited a nonlinear I{V characteristic after the device was burned in by applying a constant voltage for a rela- tively long period of time (several minutes), during which time the electrical properties eventually settled into a repeatable pattern. Some devices exhib- ited a well-de
  • 8. ned nonlinear I{V characteristic immediately, but often would fail rapidly unless operated while immersed in liquid nitrogen, probably due to excess power dissipation in the device. Two of the devices constructed showed a symmetric electrical characteristic, i.e., equal but opposite forward-bias and reverse-bias behavior. This result is shown in Figure 6.2.
  • 9. CHAPTER 7. ELECTRICALLY SYMMETRIC PPA DIODES 3 ITO PPA Aluminum Electrode Substrate ITO PPA Substrate Al Figure 7.1: Al/PPA/ITO Diode Device Construction (not to scale).
  • 10. CHAPTER 7. ELECTRICALLY SYMMETRIC PPA DIODES 4 48 32 16 Current (mA) 0 -16 -32 -48 -20 -10 0 10 20 Forward Bias (Volts) Figure 7.2: I{V Characteristic of symmetric Al/PPA/ITO Diode.
  • 11. CHAPTER 7. ELECTRICALLY SYMMETRIC PPA DIODES 5 Ln(I/V2) -2 -3 -4 0 0.2 0.4 0.6 0.8 1 1/Bias (1/Volts) Figure 7.3: Ln(I=V 2 ) vs. 1=V for the data in Fig. 6.2. The device represented in Fig. 6.2 was observed to emit light from an acti- vated electrode in both forward-bias and reverse-bias. The light was easily seen with the naked eye and judged to have equal intensities in both forward- and reverse-bias. The device failed before quantitative measurements of the emitted light could be made. Discussion The basic theory of tunneling predicts the relationship [2] I / V 2 e0 V
  • 12. d (7.1) where d is the polymer thickness. Figure 6.3 shows ln(I=V 2 ) plotted versus 1=V for the reverse-bias curve (the curve for forward-bias is virtually identical). The plot is linear above a certain voltage range (dotted line), indicating a tunneling mechanism. If we assume a triangular barrier,
  • 13. is given by [3] p 4 2m3 ' 2 3
  • 14. = (7.2) 3e~
  • 15. CHAPTER 7. ELECTRICALLY SYMMETRIC PPA DIODES 6 where ' is the barrier height and m3 is the carrier eective mass. If we assume that the eective mass equals the free electron mass, data from Fig. 6.3 results in ' = 0.07 eV. The lower voltage range in Fig. 6.3 cannot be considered a valid range for an alternative linear
  • 16. t to the excess current because the tunneling length (L = '=F) is too large for direct tunneling (L 60 A for F = 1 Volt/1000 A) to occur. It has been suggested by Raikh [4] that the excess current at low voltages is due to sequential tunneling of electrons via localized states in the gap. This theory predicts the following I{V relationship: pd I / e0 V (7.3) q 31 3 where = 4 0 2~2 3 m 4 ' 4 and 0 = ln 1 . p p is de
  • 17. ned as the probability that an electron
  • 18. nds a localized state withp an energy close to the Fermi level. Figure 6.4 shows ln(I ) plotted versus 1/ V for the reverse-bias data in Fig. 6.2. The plot is linear below a certain voltage range (dotted line), as predicted by the theory. Since neither p nor ' change with
  • 19. eld strength, the higher voltage range in Fig. 6.4 must still be explained by an alternative mechanism, such as standard tunneling described for Fig. 6.3. The electrically symmetric I{V characteristic in Fig. 6.2 can be explained for low voltages by the localized-state theory (Eq. 6.3), with defects providing the localized gap states. If the defects are amphoteric (able to accommodate ei- ther electrons or holes), it is possible to observe electrically symmetric behavior at low voltages. The symmetric I{V characteristic at higher voltages is more dicult to explain. Barriers to electron and hole injection should in principle be dierent because the work function of Al (4.0 eV) [5] does not match the electron-injection band as well as the work function of ITO (4.7 eV) [6] matches the hole-injection band. On the other hand, it is well-known that the eective work function of a material strongly depends on surface characteristics. The cleanliness of surfaces and/or the presence of insulating oxide layers can them- selves create barriers and surface states which appear to minimize dierences in work functions. In particular, it may be possible for each contact to inject elec- trons or holes, depending on the bias conditions and the meta/polymer interface properties. If both contacts have the ability to inject electrons or holes because of eec- tively equivalent work functions and the presence of surface states, a symmetric I{V characteristic due to tunneling through relatively small barriers may logi- cally follow. This possibility is dicult to evaluate because of a lack of knowledge of the details of the metal/polymer interface.
  • 20. CHAPTER 7. ELECTRICALLY SYMMETRIC PPA DIODES 7 4 2 Ln(I) 0 -2 -4 0 0.2 0.4 0.6 0.8 1 1/√V (1/√volts) p Figure 7.4: Ln(I ) vs. 1= V for the data in Fig. 6.2.
  • 21. CHAPTER 7. ELECTRICALLY SYMMETRIC PPA DIODES 8 Summary The fabrication and testing of a luminescent polymer diode has been reported and discussed. The device exhibited symmetric I{V characteristic and lumines- cence in both forward- and reverse-bias. A theory involving tunneling via local- ized gap states [4] was considered to explain excess current and electrically sym- metric behavior at low voltages. Direct tunneling from the contacts into hole- and electron-injection bands is the likely mechanism for the electrical character- istics and luminescence at higher voltages. To explain the electrically symmetric behavior at higher voltages, it is suggested that non-ideal metal/polymer inter- face properties allow the injection of holes or electrons through similar barriers from either contact. Future work will address this issue. References [1] See, for example, Synthetic Metals 55{57 (1993). [2] R. H. Fowler and L. Nordheim, Proc. Roy. Soc. London, 119A, 173 (1928). [3] S. M. Sze, Physics of Semiconductor Devices, 2nd ed., (Wiley) 1981. [4] M. Raikh and X. Wei, these proceedings. [5] J. I. Pankove, Optical Processes in Semiconductors, Dover, NY, 1975. [6] H. Antoniadis, et al., Synthetic Metals, in press.